This invention generally relates to compositions containing polymers useful in carbon dioxide processes.
Separation and catalytic reaction processes play an extremely significant role in the chemical and materials process industry. With respect to catalysis, there is currently a high level of interest directed toward catalyst systems with improved selectivity, activity, and recovery for the synthesis of a wide range of chemicals. Of particular interest are specialty chemicals particularly chiral compounds which are believed to be important to the agrochemical and pharmaceutical industries.
Catalysis processes involving complex chelating (often chiral) bisphosphine and aminophosphine ligands with precious metals such as rhodium, platinum, and palladium has received a high level of attention. The industrial application of such catalysts, however, is believed to be severely hampered in that one is often unable to recover and reuse these materials. This is highly significant in that the inability to recycle and reuse the catalysts result in processes that are often too costly to implement. Moreover, heightened environmental scrutiny provides additional motivation to recover the catalysts.
Heterogeneous catalysis potentially offers a partial solution to the above difficulties, and is widely employed in chemical commodity synthesis. Although these catalysts offer the advantage of separability, they generally do not allow for controlled design and synthesis of the immediate ligand environment. Such controlled design and synthesis is typically important for controlling catalyst selectivity and activity. In an attempt to address the above problem, the heterogenization of homogeneous catalysis has been proposed which typically involves employing polymeric or inorganic supports. See, e.g., J. M. Tomas et al., Angew. Chem. Int. (1994), 33, p. 913, (1994); R. D. Srivastava, Heterogeneous Catalytic Science, CRC Press, Boca Raton, Fla., (1988); D. C. Bailey et al., Chem. Rev. (1981) 81, p. 109; R. T. Peltonen, et al., Ind. Eng. Chem. Res. (1994), 33, p. 235; and M. G. McGrath et al., Chem. Rev. (1995) 95, p.381. In general, these efforts are carried out in an attempt to combine the advantages of homogeneous catalysis (e.g., ability to control selectivity and activity through designed ligands, controllable ligand environment, and firm mechanistic understanding) and heterogeneous catalysts (e.g., ease of separation). Various catalysts heterogenized with inorganic and organic supports have been developed. However, they have often been plagued by mass transfer problems. Low selectivity has also been observed in these systems.
Conventional separation processes typically involve aqueous and organic media, and as a consequence waste products comprising these materials are often generated.
In view of the above, there is a need in the art for chemical processes that could take place in a potentially more environmentally favorable medium.
In one aspect, the invention provides a method for carrying out a catalytic reaction in carbon dioxide. The invention comprises contacting a mixture with a catalyst bound to a polymer wherein the reactant interacts with the catalyst to form a reaction product. The fluid mixture comprises at least one reactant and carbon dioxide.
The polymer that is employed in accordance with the invention may be either soluble or insoluble in the carbon dioxide. Such polymers preferably comprise at least one xe2x80x9ccarbon dioxide solublexe2x80x9d (xe2x80x9ccarbon dioxidephilicxe2x80x9d) segment that has an affinity for carbon dioxide. Polymers that are insoluble in carbon dioxide are typically crosslinked. In various embodiments, these polymers may be considered xe2x80x9cswellablexe2x80x9d in the carbon dioxide as defined in greater detail herein, although other types of polymers may be employed.
In another aspect, the invention provides a composition of matter comprising carbon dioxide and a polymer present in the carbon dioxide. The polymer has bound thereto a catalyst at a plurality of chains along the length of the polymer.
In another aspect, the invention provides a method of separating at least one component from a fluid mixture. The method comprises contacting a polymer with a fluid mixture comprising at least one component and carbon dioxide. The carbon dioxide interacts with the polymer and separates from the fluid mixture such that the fluid mixture has an increased concentration of the at least one component.
These and other aspects are provided by the present invention.